I think it's important to point out it's not really accurate to say it's a circulatory OR nervous effect when in fact the passout effect (syncope) is the result of a feedback loop involving both (a systemic effect).
We're talking about an effect that is occurring in two separate systems that feed into each other (circulatory and nervous) simultaneously, not one after the other, from a SINGLE external force (neck strangulation).
Applying the proper neck pressure in the right spot is essentially causing a big disagreement with those two systems, and the time you spend asleep is the time it takes for them both to normalize.
Otherwise you get into the "chicken and egg" argument of what comes first, constricted arteries and HIGHER blood pressure OR baroreceptors/vagus response and the resulting LOW PRESSURE, when in fact these are atomic events (i.e. they happen at the same time). So it makes sense for creativo to say "pressurizing the neck restricts bloodflow" because that is correct, but not the sole reason for syncope because that effect can only come when both the nervous and circulatory responses to strangulation "kick in".
So putting this in science-ey terms:
- More physical pressure on the neck arteries = high BP = faster vagus response = (low BP) + (baroreceptorized, poor oxygen content blood) = sleep
- Closer physical pressure to vagus/sinus = faster vagus response = (low BP) + (baroreceptorized, poor oxygen content blood) = sleep
High blood pressure causes the vagus response, which is to lower pumping rate of the heart rapidly (and thus pressure). You can get a blood pressure drop and syncope from having generally high blood pressure, or just COUGHING HARD. The vagus is what tells your heart not to explode while it tries to pump all that blood around your (now pressurized) circulatory system.
"hey buddy there's some congestion up ahead...you might want to slow down for a minutes...that's right...lay back...try to enjoy this..."Local blood pressure around the vagus definitely plays a role, everyone can (hopefully) see from the diagrams that the vagus connects right into the arteries. So the closer constriction is to the vagus, the more effective the choke.